The art is replete with flap wheel assemblies comprising a central hub, a plurality of flap members that extend the length of the hub, and means for holding edge portions of the flap members in spaced relationship around the peripheral surface of the hub with the width of the flap members (e.g., pads of abrasive material or brushes) projecting outwardly of the hub to afford, upon rotation of the hub about its axis, engaging distal portions of flap members with a surface of a work piece to abrade or otherwise finish the surface. U.S. Pat. Nos. 2,821,819; 2,871,632; 2,921,329; 3,533,198; 3,645,049; 3,869,833; 4,133,146 and 4,217,737 provide illustrative examples. In many such flap wheel assemblies the flap members are rectangular and are attached so that the flap members extend parallel to the axis of the hub and in use the entire width of a flap engages a work piece at once. As is illustrated in U.S. Pat. Nos. 2,921,329 and 4,217,737, however, the flap members may alternately be disposed in a helical pattern along the periphery of the hub which is known to quiet the operation of the flap wheel assembly due to the sequential engagement of each flap with a work piece. Straight flap members have also been disposed on a cylindrical hub slightly out of parallel with its axis (i.e., angled at about six degrees) to provide a small measure of sequential engagement between the flap members and a work piece.
While flap wheel assemblies of the type described above can provide uniform finishing effects when used on planar surfaces, they are not as effective when used to finish arcuate convex surfaces such as a generally cylindrically convex metal cover for a casket or a side panel for an automobile.
An arcuate convex surface 10 has been finished using a flap wheel assembly 11 (illustrated in FIG. 1 of the drawing) including flaps 12 disposed parallel to an axis 13 of a cylindrical hub 14, which flaps 12 have projecting portions shaped to provide distal edges 15 that correspond to the arcuate shape of the surface 10 to be finished. The central cross sections of such flaps 12 are more stiff than their end cross sections, however, so that a uniform finish may not be achieved across the width of the arcuate convex surface 10. Also, there is little projecting flap material along the central cross sections of the flaps 12 so that the flaps 12 wear out quickly compared to flaps that have uniform widths along their lengths. An arcuate convex surface 10 has also been finished using a flap wheel assembly 16 (illustrated in FIG. 2 of the drawing) including flaps 17 disposed parallel to an axis 18 of a hub 19, which the flaps 17 are of of uniform width and are arcuate along their entire lengths to provide distal edges 20 that generally correspond to the shape of the surface 10 to be finished, and the central cross section of the hub 19 is reduced in diameter to receive the uniform width of the flaps 17. While the flap wheel assembly 16 produces suitable finishing results, such arcuate flaps 17 are specialty items that are suitable for use on only a small range of arcuate surfaces and can not also be used on cylindrical hubs intended to finish planar surfaces. Thus their use would significantly increase the different types of flaps that must be made and stored. Also, more waste of materials is incurred in the production such arcuate flaps 17 than in the production of rectangular flaps.